There are a number of polyamideimide (PAI) and polyimide (PI) resins currently used in the electronic applications industry. These can be employed as protective coatings for high temperature applications or as insulating coatings for applications where good thermal shock or damp heat resistance is imperative. PAI and PI systems are also very flexible, which can be advantageous in thin film applications where substrates are often folded or flexed.
These PAI or PI coatings are generally thermally curing and do not have any UV sensitivity built into the formulation. Application of these coatings is therefore limited to direct imaging applications where the desired image is created directly onto the substrate, for example by screen printing.
There is a limit to what can be achieved in terms of image resolution using direct imaging techniques. Higher resolution images are usually achieved by using liquid photo-imageable (LPI) systems, where the resolution is determined by the phototool used to create the desired image. In order to create LPI coatings, formulations preferably encompass both thermally curing and UV curing elements.
There are several examples in the prior art of polyamideimide and polyimide polymers being modified to incorporate UV sensitivity to create photo-imageable resins, but these focus on grafting the UV functional groups onto the polymer backbone. This approach can lead to unstable materials with a short shelf-life, and the resultant polymers can be difficult to utilize in many electronic applications because of the complex processing requirements for subsequently printed inks.
Thermally curing polyamideimide and polyimide resins have limited compatibility in conventional ink formulations as they are nitrogen containing materials which are incompatible with typical unsaturated UV acrylates. When most UV acrylates are introduced to the PAI or PI resin systems, if they are not immediately incompatible, they tend to gel very quickly, making the composition unusable for practical applications.
The preparation of polyamide, polyimide, polyamideimide, and polybenzimidazoles is described in the art. See, for example, U.S. Pat. No. 8,269,358 which describes the use of bis(aminophenol) as a raw material for the preparation of polyamide and polyamideimide resins. The resins can be used as a photosensitive positive-type photo resist. U.S. Pat. No. 5,703,199 discloses a process for preparing polyamides, polyimides, and polybenzimidazoles.
U.S. Pat. No. 6,261,741 discloses a photosensitive heat resistant resin containing a polyamideimide (PAI) resin, an organic solvent for dissolving the PAI, an acrylic monomer or oligomer having at least two polymerizable double bonds, and a photoinitiator. The resin is used to make a heat resistant insulating film that can be patterned.
US 2013/009223 describe a multilayer film containing layers of polyamide and polyester. The films are prepared by co-extruding the different layers.
US 2004/0180286 disclose a photosensitive resin composition suitable as a material for a protective or insulating film of electronic components. The resins contain a polyamide or polyamideimide resin, and at least one photopolymerizable compound, selected from a silane coupling agent or a photopolymerizable unsaturated monomer having at least 5 photopolymerizable unsaturated bonds per molecule.
U.S. Pat. No. 8,871,422 disclose a negative-type photosensitive resin composition that can be used as a photoresist. The resin contains a component (A), which is a polymer having a terminal phenolic hydroxyl group, examples of which are polyimide, polyoxazole, polyamideimide, polyamide, polyamic acid, polyamic acid ester, and polyhydroxamide. The resin also contains a component (B), which is an acid-generating photoinitiator; and a component (C) which is a compound that can be crosslinked or polymerized by an action of the acid. The acid generator B generates acid by irradiation by UV light. The acid that is generated catalyzes the thermal reaction of the phenolic hydroxyl group on component A with component C, which contains a functional group that can react with A. Typical functionality would be a methylol group, which would react with A with the liberation of water. There is no free radical polymerization in this approach, and the formulation suffers from lack of resolution. Nitrogen containing ethylenically unsaturated monomers are not used.
KR 2006-0124859 provides a solder resist composition for printed circuit boards. The solder resist composition comprises a UV-reactive acrylic monomer, a photoinitiator, and an organic solvent. The composition further comprises a polyamideimide resin. The composition is dried to form a film, and the dried film is applied on the circuit board.
JP 2004-258544 discloses a retardation film that exhibits good durability against UV rays, and excellent transmittance for visible light. The film is prepared by mixing a UV absorbent into a polymer. The polymer can be, for example, polyamide, polyimide, polyester, polyether ketone, polyamideimide, polyesterimide, or the like.
JP 2012-077144 discloses a polyamideimide solution and a polyamideimide film that exhibit good heat resistance, solubility in an organic solvent, and a low line thermal expansion property. The polyamideimide resin can be applied to a variety of substrates, such as glass, metal, metal oxide, and single crystal silicon.
KR 2009-0062498 describes a molecular composite of polyamidimide and polyimides exhibiting heat resistance, high strength, low dielectric constant, good optical characteristics, and durability. The composite can be used as insulating coating materials of fibers, film, casting product, foam, adhesive, heat-resistant coating material, and wires.
KR 2012-0023545 provides a photo-sensitive resin composition, into which are mixed purine derivatives. The resin is at least one selected from polyamide acid, polyamide acid ester, polybenzoxazole, and polybenzthiazol. The resin can be used to form a cured relief pattern on a semi-conductor device.
JP 2008-260839 discloses a negative-type photosensitive resin composition comprising a polyamideimide. The composition is heat cured to form a film.
JP 4736863 discloses a positive photosensitive polyamideimide resin composition having good sensitivity, resolution, adhesion in development, and heat resistance. The composition comprises a polyamideimide, a compound which generates an acid under light, and a solvent.
JP 3823411 provides a photosensitive resin composition having good adhesiveness and wet heat resistance. The resin is obtained by incorporating at least either an epoxidized polyamide resin or an epoxidized polyamideimide resin and a photopolymerization initiator as essential ingredients in the composition.
There are many other industrial applications for which a photo-defined UV/thermal system would be advantageous. These include, but are not limited to, printed electronics, photovoltaic modules, semiconductors, automotive parts, aerospace, X-ray and 3D printing. Consequently, there is still a need in the art for a UV and thermally curing photo-defined system that is stable.